[ABC265A] Apple

Problem Statement

A fruit store sells apples.

You may perform the following operations as many times as you want in any order:

• Buy one apple for $X$ yen (the currency in Japan).
• Buy three apples for $Y$ yen.

How much yen do you need to pay to obtain exactly $N$ apples?

Constraints

• $1 \leq X \leq Y \leq 100$
• $1 \leq N \leq 100$
• All values in input are integers.

---

Input

Input is given from Standard Input in the following format:

$X$ $Y$ $N$

Output

Print the answer as an integer.

---

Sample Input 1

10 25 10

Sample Output 1

85

Buy three apples for $25$ yen three times and one apple for $10$ yen, and you will obtain exactly $10$ apples for a total of $85$ yen.

You cannot obtain exactly $10$ apples for a lower cost, so the answer is $85$ yen.

---

Sample Input 2

10 40 10

Sample Output 2

100

It is optimal to buy an apple for $10$ yen $10$ times.

---

Sample Input 3

100 100 2

Sample Output 3

200

The only way to obtain exactly $2$ apples is to buy an apple for $100$ yen twice.

---

Sample Input 4

100 100 100

如果单独买三个苹果，比一下买三个苹果的价格还要小，那就一个一个苹果买。
否则，就尽量三个三个买，买完剩余的在一个一个买
```cpp
#include
using namespace std;
int x,y,n;
int main()
{
scanf("%d%d%d",&x,&y,&n);
if(3*x<=y)
printf("%d",x*n);
else
printf("%d",y*(n/3)+n%3*x);
}
```